This application claims the priority of German application 19945259.8, filed Sep. 21, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for electroacoustic sound generation in a motor vehicle.
The control of sound is a vehicle component is based on the principle that the vehicle occupants should be offered a high measure of acoustic comfort, with particular value being attached to a low noise level. On the other hand, the driver should also be able to exactly recognize the operating state of the engine. For this purpose, feedback of the driving sound, particularly feedback of the engine sound, is advantageous. In other respects, emission regulations (including noise emission regulations) must be met.
To resolve these conflicting aims it is known in the art to modify the noise in the passenger compartment by passive adjustment measures, e.g., by aggregate bearings.
Furthermore, in addition to good sound insulation, the synthetic generation of passenger compartment sounds, or the storing of sound components and electroacoustic playing into the passenger compartment, are also known in the art (cf. European Patent EP 0 469 023 B1, German reference DE 27 34 948 A1).
The exhaust system and the intake tract are sources which have strong load dependency. However, a general increase in the sound emitted by these excitation sources is not an appropriate solution due to the aforementioned emission and external noise regulations. Additionally, the introduction of these sound components into the compartment is largely inhibited by high body insulation, which is necessary to reduce wind and rolling sounds and to suppress interfering mechanical engine sound components. Although a deliberate mechanical introduction into the passenger compartment is possible in principle and known in the art (German references DE 44 35 296 A1, and DE 42 33 252 C1), it has proven to be disadvantageous with respect to costs and arrangement within the vehicle.
A purely synthetic production of an engine sound has also proven to be disadvantageous since, as a rule, it does not give the perception of an absolutely authentic engine sound.
German Patent DE 198 45 736 A1 therefore proposes to detect the sound pressure in the intake or exhaust tract of an internal combustion engine, to process it and to introduce the signals thus generated into the passenger compartment. The intake and exhaust tracts are acoustic sources that are particularly load-dependent. Even very simple embodiments can thus convey relatively faithful acoustic signals to the passenger compartment. Using filtering elements in a signal processing unit of the above-described device allows for variation in the sound characteristic. There are limits, however, with respect to this ability to modify the sound composition. For example, those frequency spectrums that are not contained in the signals supplied by the sound pressure sensor cannot be generated.
Thus, the object of the present invention is to improve an initially described device for electroacoustic sound generation in such a way as to ensure a sound generation that is as variable as possible but nevertheless authentic.
Accordingly, a synthesizer is added to a device such as the one disclosed by DE 198 45 736 A1. This synthesizer artificially produces signals or sounds and adds these sound components to the signals generated from the sound pressures. This makes it possible to introduce sounds into the passenger compartment with frequencies that do not occur in the intake or exhaust tracts.
To produce a particularly authentic engine sound, it was found to be advantageous to generate sinusoidal frequencies that can be traced to the rotational frequencies of the driving engine. In particular, one or several sinusoidal frequencies corresponding, for example, to a half-integral and/or integral multiple of the engine speed can be generated.
Adding synthesized sound components to the sounds that are generated via the sound pressure sensor makes it possible to produce an overall impression that is desirable from the perspective of a sound designer and still sounds authentic.
In one embodiment amplitudes and phases of sinusoidal frequencies are first stored. These amplitudes and phases are added in a table as a function of the rotational speed of the driving engine. Depending on the engine speed, the corresponding amplitude and phase values can be read out of the table, and the synthesizer can generate signals as a function thereof. This makes it possible to achieve a sound characteristic that is adapted to the speed. Of course, the amplitude ratio of the various pure tones decisively determines the overall sound characteristic. The amplitude of the signals to be played by the synthesizer can also be influenced by, for example, the throttle position, the accelerator pedal position, or other load signals. Particularly by taking into account signals that are coupled to a load, it is possible to achieve load-dependency of the generated sound as well.
According to an alternative embodiment, the signal from the sound pressure sensor itself can serve as the input variable for the synthesizer. This input signal is also load-dependent in a particular manner.
If a certain sound characteristic is to be achieved as a function of different vehicle operating conditions, the amplitude and/or phase ratios of the individual sounds must be modified. In addition to control via the throttle position, the accelerator pedal, the rotational speed of the driving engine, and the vehicle speed, other parameters, such as the kickdown position, gear selection or, for example, a signal indicating whether the convertible top is open or closed can be used to determine the amplitude and/or phase ratios. Several tables can be provided from which values can be selected as a function of these or other vehicle parameters.
In a particularly advantageous embodiment, a vehicle thrust is detected and a matching sound is created. For example, during the transition to a thrusting operation, a slowly surging sound can be produced. It is also possible to produce a stochastic noise during the detected thrust (putt-putting, muttering) and play. To this end a unit to detect push operation must be provided. Depending on the evaluation signal, a characteristic acoustic pattern must then be selected for this push operation and a signal must be supplied to the synthesizer. The synthesizer then produces a desired sound in push operation.
Overall, the present invention provides a further improvement of the sound in a passenger compartment, particularly in view of the variability with respect to different vehicle operating conditions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.